When we write in screenplay format, we need to keep in mind the key formatting elements;

Scene Headings: Placing the actors in space and time

Action: What physical actions people can see on screen; sharing emotions and causing plot shifts

Character: Who is speaking and when

Dialog: What lines actors speak

Adding a title page is something you should do once you're going to share your screenplay. We can do this in Celtx with ease. Here are some images (in order) that show you how to add and edit a title page in Celtx.